There has been known to the art a filter press of the type in which a plurality of filter plates are arranged in parallel between a pair of heads and on a pair of parallel guide rails supported by machine frames and in which the individual filter plates are connected one to another by loose link means between the pair of heads so that they may be assembled or separated at same time. The filtering operation is carried out when the filter plates are assembled, and the cake-discharging operation is carried out through movement of filter cloths when the filter plates are separated. Filter presses of such type are disclosed in U.S. Pat. No. 3,807,567, British Pat. No. 1429855, German Pat. No. 2309778, and Canadian Pat. No. 996470, for example.
In any such filter press, liquid to be filtered or slurry is fed under high pressure for filtration when the filter plates, adapted to be folded and unfolded in accordion pattern, are folded or assembled, and if each filter plate has diaphragms provided on its surfaces for pressing the cakes, the diaphragms are subject to pressure. Therefore, it is essential that the individual filter plates arranged between the pair of locking heads must be held in tightly locked condition so as to withstand such high pressure when they are assembled together.
Such filter press also requires that in order to provide a larger filtration area there must be a larger number of filter plates.
Therefore, the following problems have been found with filter presses of such type.
One problem is that increasing the number of filter plates to provide a larger filtration area involves an increased distance of stroke of the piston rod in the hydraulic cylinder means for separating, assembling and tightening the filter plates entrained on the pair of guide rails, such increased distance of stroke requiring much larger space. Another problem is that in order to prevent the piston rod from buckling due to the increased distance of stroke, the piston rod must have its diameter and weight increased at same time, which means considerable increase in costs.
One approach for solving these problems may be that the pair of heads are adapted to be movable and that the hydraulic cylinder is disposed between one of the heads and one of the frames, with ready-to-engage latch means provided between the other head and the other frame or a guide bar, said latch means being adapted to unretreatably hold said other head in position on the guide bar. With a filter press of such arrangement, however, there is a still a problem that, as is the case with a filter press of the type disclosed in U.S. Pat. No. 3,807,567, wherein one of the heads is stationary, that is, fixed to a frame supporting guide bar, and the other head is movable, considerable time is required in assembling or separating all the filter plates because the filter plates are assembled or separated in regular sequence from one end side through the movement of the movable head, and therefore, that the time requirement for assembling and separating the filter plates, or so-called miscellaneous cycle time that is not directly concerned with filtering operation, will increase as the number of filter plates is increased to provide increased filtration area, which will rather result in decreased filtration efficiency. Inasmuch as the means for folding and unfolding the assembly of filter plates in accordion pattern comprise one head for assembling and separating the filter plates over the entire space for the purpose and drive means therefor provided on the head and since means for tightening the filter plates, as assembled, under high pressure comprise a hydraulic cylinder disposed on another head, the above problem is unavoidable, even if the stroke of the hydraulic cylinder could be minimized.